Category Archives: EuroSun2008-4

Contribution of the Solar Thermal System to the Building Energy Performance — specific aspects of the Portuguese legislation

3.1. Short descriptions


The Portuguese legislation transposing the EU Directive 2002/91/CE, includes a Solar Thermal Obligation, imposing the usage of solar thermal collectors for hot water preparation if there are favourable conditions for exposure (if the roof or cover runs between SE and SW without significant obstructions) in a base of 1m2 per person. The energy necessary for the preparation of hot water constitutes one of the terms for evaluation of energy performance of the building, as well as, the heating and cooling loads of the building, according to:

This term is calculated per apartment area, Ap, and the term Qa is the heat demand for hot water preparation given by in equation (8) and it is equivalent to Qsol, use. pa is the efficiency of the conventional heating equipment used for hot water preparation (backup system). The term Eren is any other renewable energy that is used for hot water preparation or that substitutes the thermal solar system, according to the permitted cases in the legislation.

Qa =(MAQS • 4187-AT • nd )/(3600000)[kWh/yr] (8)

The mass of water to be heated is equivalent to a volume of 40 l per conventional occupant. Also the collector area to be installed is a function of the number of conventional occupants, considering 1 m2 per occupant. Conventional occupants are a function of the home typology, i. e., the number of rooms, according to Table 1.

In equation 8 the value of AT is equal to 45°C, i. e., Tload — Load temperature — 60°C and Tcold — Temperature of cold water (mains water) — 15°C.

The value nd is the number of days where hot water preparation is needed. In the case of residential buildings is equal 365.

Tablel — Number of conventional occupants in an appartment

Apartment typology

T0, T1





N. of conventional occupants






The term Esoiar is calculated using the software tool developed by INETI and called SolTerm [2], whose characteristics were shortly described in section 2.2.. This term is equivalent to QW, sol, out.

2. Results

For comparison of the two methodologies default values introduced in section 2. were used. The comparison is based on the value Qsol, out, m.

Calculations were made for one location only, Lisbon, and the monthly values of Esol, in were derived from SolTerm data base. Two flat plate collectors, one selective and one non-selective, were considered. In Table 2, the parameters of the two collectors are listed.

Table 2 — Characteristic parameters of the collectors used for comparison purposes.







[W/K m2]


[W/K2 m2]



A(selective flat plate)






B(non-selective flat-plate)






Calculations of Qsol, out were made and the yearly values were compared for different system configurations considering that the system load volume varied according to the apartment typologies given in Table 1. Results are shown in Table 3.

Table 3 — Energy delivered by the solar thermal system for hot water preparation.

Qsol out vear [KWh]





area 2


Vload Vstore


EN 15316

SolTerm 5.0


Collector A

T2 (3 m2)

2 col x 2.3 m2





T3 (4 m2)

2 col x 2.3 m2





T4 (5 m2)

3 col x 2.3 m2





T5 (6 m2)

3 col x 2.3 m2





T6 (7 m2)

4 col x 2.3 m2





Collector B

T2 (3 m2)

2 col x 1.65m2





T3 (4 m2)

3 col x 1.65m2





T4 (5 m2)

3 col x 1.65 m2





T5 (6 m2)

4 col x 1.65m2





T6 (7 m2)

5 col x 1.65 m2





The comparison between the two methods shows a strong difference as a function of the collector type, i. e., its efficiency parameters. While for a selective collector, the results obtained with the two methods have differences lower then 2%, in the case of the non-selective collector, differences can be of the order of 10%, with underestimation by the methodology of the standard EN 15316-4­


To explain this discrepancy, it is necessary to recall that the methodology of EN 15316-4-3 is based on f-chart method [6] and that this method is a result of correlations derived from several simulations using a specific configuration system and TRNSYS programme [8]. In reference [6] the range of design parameters is indicated. Two of them are dependent on collector efficiency parameters; 0.6 < (xa)n <0.9 and 2.1 < UL < 8.3 W/K m2. For flat plate collectors (xa)n =p0 and UL is the heat loss coefficient not dependent on temperature. In the case of the non-selective collector, using the efficiency curve with parameters a1 and a2 to determine a linear approximation (up to 0.07), a UL of 8.4 W/K m2 is obtained, showing that it is outside the limit of values considered in the correlations of the f-chart method.

Results considering different ratios of storage tank volume and collector area were also obtained as can be seen in Table 4 for the case of selective collector listed in Table 2.

Table 4 — Solar fraction (%) calculated for thermal solar systems with selective collectors.

Vstore = 1000 l

Vstore = 2000 l

Vstore = 3000 l

EN 15316

SolTerm 5.0

EN 15316

SolTerm 5.0

EN 15316

SolTerm 5.0

100 l/m2







75 l/m2







50 l/m2







25 l/m2







In this case, the comparison is presented by the value of yearly solar fraction. The differences using both methodologies are not dependent on the ratio between storage volume and collector area.

3. Conclusion

The European Standard EN 15316 (part 4-3) [3] includes a methodology for calculation of the energy delivered by a thermal solar system for hot water preparation based on the f-chart method

[6] . This methodology is easy to apply and can even be implemented in an Excel Sheet.

The in the work developed, a comparison of this calculation procedure with the methodology adopted in the Portuguese legislation [1] was presented, i. e., calculation using the SolTerm programme [2]. SolTerm 5.0 was the version used for comparison purposes. It is possible to see that the results obtained with both methodologies are comparable when the collectors used are of the type flat plate selective collectors.

If non selective flat plate collectors are considered the differences between the two methodologies can be of the order of 10%, where EN 15316-4-3 [3] corresponds to an underestimation of the energy delivered by the solar thermal system. The possible explanation for this difference is the fact that the methodology of EN 15316.part4-3 [3] is based on f-chart method [6], which has application limits dependent on the collector efficiency parameters.

Further investigation is necessary in the case where the collector efficiency is higher then the typical values for selective flat plate collectors, as is the case of evacuated tube collectors.

Possibility of adoption of the methodology of EN 15316 in the calculation of solar space heating systems is limited due to the fact that the standard only presents correlation coefficients for one type of space heating systems — direct floor heating system.

Подпись: A ai a2 Esol,in fst Im IAM QW,sol,out QH,sol,out QHW,sol,out Подпись:Подпись:collector aperture area according to EN 12975-2 [m2]

heat loss coefficient of solar collector related to the aperture area according to EN 12975-2 [W/Km2] temperature dependent heat loss coef. related to the aperture area according to EN 12975-2[W/K2 m2]

Incident solar energy on the plane of the collector array [kWh/m2] storage tank capacity correction factor [-]

average solar irradiance on the collector plane during the considered period [W/m2]

incidence angle modifier of the collector = К50(та), from the collector test standard EN 12975-2 [-]

Heat delivered by the thermal solar system to domestic hot water distribution [kWh]

Heat delivered by the thermal solar system to space heating distribution system [kWh]

Total heat delivered by the thermal solar system to space heating and domestic hot water distribution systems [kWh]

Auxiliary electrical energy for pumps and controllers [kWh]

recoverable auxiliary electrical energy for pumps and controllers. Part of the auxiliary electrical energy, which is recoverable for space heating [kWh]

internally recovered auxiliary electrical energy for pumps and controllers. Part of the auxiliary electrical energy, which is transferred as useful heat to the thermal solar system [kWh]

non recoverable auxiliary electrical energy for pumps and controllers. Part of the auxiliary electrical energy, which is neither recoverable for space heating nor transferred as useful heat to the thermal solar system [kWh]

Total thermal losses from the solar system [kWh]

thermal losses from the thermal solar system, which are recoverable for space heating [kWh]

Non recoverable thermal losses from the thermal solar system. Part of the total thermal losses, which are not recoverable for space heating [kWh]

monthly heat use applied to the thermal solar system, usually termed as heat demand [kWh] temperature needed for hot water preparation [°С] temperature of cold water [°С] length of the month [h]

heat loss coefficient of the collector loop (collector and pipes) [W/(m2.K)]

Uoop p overall heat loss coefficient of all pipes in the collector loop, including pipes between collectors and array

pipes between collector array and solar storage tank [W/(m2.K)]

Vload Daily volume of hot water needed for hot water preparation [l]

n0 zero-loss collector efficiency factor obtained according to EN 12975-2 and related to the aperture area [-]

nloop efficiency factor of the collector loop taking into account influence of the heat exchanger [-]

0 re/ reference temperature depending on application and storage type [°С] average outside air temperature over the considered period [°С]

e, avg

p water density [kg/liter]


[1] RCCTE, Portuguese Thermal Performance Building Code (Decreto-Lei n.° 80/2006, DR 67 SERIE I-A, 2006-04-04),

[2] SolTerm, Version: 5.0.2 — 27th April 2007, (Authors: Ricardo Aguiar and Maria Joao Carvalho), CD — ROM distribution, ISBN 978-972-676-205-8

[3] EN 15316-Part 4-3 (2007), Heating systems in buildings. Method for calculation of system energy requirements and system efficiencies. Part 4-3: Heat generation systems, thermal solar systems.

[4] EN ISO 9488 (1999), Solar Energy — Vocabulary

[5] EN 12976 (2006), Thermal solar systems and components — Factory made systems — Part 2: Test methods, European Standard.

[6] J. A. Duffie and W. A. Beckman, Solar Engineering of thermal processes, John Wiley and Sons, 3rd edition, 2006, Chapter 20 — Design of Active systems: f-chart.

[7] EN 12975 (2006), Thermal solar systems and components — Solar collectors — Part 2: Test Methods, Section 6.1. European Standard.

[8] TRNSYS: A Transient System Simulation Program (Version 15), S. A. Klein, W. A. Beckman and P. I. Cooper, Solar Energy Laboratory, Madison Wisconsin, 1998.

Passivhaus proposal to include the Mediterranean conditions

Milder winter and hotter summer climates suggested a set of modified conditions where limits to winter and summer demands are defined minimising life-cycle costs and considering local construction. Also comfort requirements needed to be met as defined by EN 15251 (2007). Lastly, country or climate specific low energy solutions proposed require to meet the energy and comfort requirements in many, if not all situations. Other solution sets, if not explicitly identified by the standard, would comply with the standard as long as the comfort and energy limits were achieved. A thorough energetic analysis under these climatic conditions demonstrated a much less necessity to promote reduced air infiltration rates or pre-heat air intake. Then the revised Passivhaus definition proposed under the Passive-On project must verify the following guidelines:

• Heating criterion: The useful energy demand for space heating does not exceed 15 kWh per m2 net habitable floor area per annum.

• Cooling criterion: The useful, sensible energy demand for space cooling does not exceed 15 kWh per m2 net habitable floor area per annum.

• Primary energy criterion: The primary energy demand for all energy services, including heating, domestic hot water, auxiliary and household electricity, does not exceed 120 kWh per m2 net habitable floor area per annum.

• Air tightness: If good indoor air quality and high thermal comfort are achieved by means of a mechanical ventilation system, the building envelope should have a pressurization test (50 Pa) result according to EN 13829 of no more than 0.6 ach-1. For locations with winter design ambient temperatures above 0 °C, a pressurization test result of 1.0 ach-1 is usually sufficient to achieve the heating criterion.

• Comfort criterion room temperature winter: The operative room temperatures can be kept above 20 °C in winter, using the above mentioned amount of energy.

• Comfort criterion room temperature summer: In warm and hot seasons, operative room temperatures remain within the comfort range defined in EN 15251. Furthermore, if an active cooling system is installed, it should be possible to keep the room temperature below 26 °C.

As the Passivhaus has a reduced amount of energy consumption for heating and cooling, it is quite often neither practical nor economical to introduce an active system, in particular for cooling. On this assumption the proposed standard adopts the adaptive comfort theory against the more constrained Fanger approach appropriate for climatised spaces. Unlike the former, method the adaptive theory claims that upon discomfort people will react in order to restore the previously comfortable condition. In practical terms an immediate energy reduction is expected as the cooling set point is set to a higher temperature and the range of comfort temperatures is wider. Several surveys showed that people’s degree of satisfaction is strongly correlated with the outside temperature and the memory of recent temperatures. The adaptive comfort method applies to non air-conditioned or naturally ventilated buildings. [4, 5]

Traditional Mediterranean architecture often makes use of its strong building inertia, coupled with night-time natural ventilation to reduce the swing and the peak of indoor temperatures. The generalised scepticism among builders around the highly airtight buildings also promotes a variation of the German standard to combine a strong inertia with naturally ventilated buildings.

2. Passive strategies

Modelling and Performance Study of a Building Integrated Photovoltaic. Facade in Northern Canadian Climate

V. Delisle

CANMET Energy Technology Centre-Varennes, Natural Resources Canada
Varennes, Quebec, Canada J3X 1S6, veronique. delisle@nrcan. gc. ca


A model was developed to predict the electrical and thermal performance of different configurations of double-glazed and triple-glazed BIPV fenestration systems. Simulations showed that using a PV laminate as the middle pane as opposed to the outer pane reduced the amount of electricity generated by more than 22%, but led to slightly warmer inner pane temperature. This last characteristic can be beneficial in artic climates since it can contribute to reduce perimeter heating requirements. The multi-glazing BIPV systems modelled were also compared with non-vision sections of a curtainwall faqade in three different Canadian cities. These substitutions had little effect on the space cooling load, but increased the space heating energy requirements by 8.9-10.6% and 4.6-5.3% for double-glazed and triple-glazed curtainwall assemblies, respectively.

Keywords: Curtainwall, Photovoltaics, BIPV

1. Introduction

Over the past years, building-integrated photovoltaics (BIPVs) have witnessed a significant increase in interest as a technology approach for incorporating PV electricity production in buildings. One of the reasons to explain this gain in popularity is that BIPV are more architecturally pleasing than rack-mounted PV systems. Furthermore, they can be considered to have lower installation cost when used to replace expensive cladding or roofing materials [1].

Recently, designs have begun integrating PV semi-transparent laminates into curtainwall constructions [2] and skylights [3]. These laminates consist of opaque PV cells encapsulated with EVA in between two layers of transparent glass sheet. The level of transparency is determined by the PV density, which is the portion of the PV laminate area covered by PV cells, and has a direct influence on the building solar heat gain, natural daylighting, and the amount of electricity generated. Research on the integration of PV into windows has mainly focused on the impact of the different fenestration parameters on buildings energy consumption. Wong et al. [4] studied numerically and experimentally the roof integration of a double-glazed semi-transparent PV window in a residential building. For a PV density of 50%, reductions in overall energy consumption in the order of 3% and 8.7% were observed compared to a standard BIPV roof for the hottest and coldest climate studied, respectively. When the PV density was increased to 80%, the cells were found to heat up more, decreasing the electrical conversion efficiency of crystalline cells. For both 50% and 80% PV density scenarios, replacing a BIPV roof by BIPV semi­transparent windows reduced the annual heating energy requirements but increased the cooling load during the summer. Fung et al. [5] developed and validated a one-dimensional transient model of a semi-transparent BIPV laminate in Hong Kong. Compared to clear glass, BIPV laminates with

cell densities of 20% and 80% were found to reduce the annual total heat gain by approximately 30% and 70%, respectively.

This paper aims at evaluating the performance of five curtainwall constructions in Canada with multi-glazed BIPV assemblies used as the non-vision sections of a building fa9ade. To achieve this objective, an analytical model was first developed to estimate the BIPV systems thermal resistance and electricity production. Then, simulations were performed to assess their impact on a building space heating and cooling loads when combined with curtainwall vision sections to form a fa9ade.

PV-cells and design

Because poly-crystalline silicon PV-cells are cheaper than mono-crystalline silicon PV-cells and still has a high efficiency these are used for the proto-types of the PV-windows. Silicon wafers are usually not transparent. Therefore the project group has worked with variations in the design of the PV-pane, e. g. the size of the silicon wafers and carving of patterns within the PV-cells, which helps to transmit more daylight through the facade, cf. figure 1. The shaping of the design adds a degree of freedom for architects to work with daylight in building design. But this degree of freedom will raise the price, reduce the total area of the PV-cells in the window and hence reduce the electricity output of the PV-window. Therefore this has to be made as an additional choice to the standard PV-pane. The design of the PV-window must reflect the desire for daylight distribution and the electricity production. Figure 1 illustrates some of the degrees of freedom in placement and carving of the PV-cells in the pane.


Figure 1. An illustration of different possibilities in placing the PV-cells in the pane.

Summer Counter Effective Human Intervention in Fenestration Shading Strategy

2.2. Results of Summer Shading Simulation Profiles

The results from computer building simulations for the summer shading profiles are analyzed and assessed with the same procedure as for winter. The optimum fenestration profile for summer as defined below is taken as the basis in these series of combinations.

a) Optimized Fenestration Shading Strategy for Summer

The optimised fenestration strategy for summer, derived in previous work [1], is outlined as having all glazed area shaded during the day time to obtain minimum solar gains and hence comfort indoor conditions ranging between 23.3 — 25.4 degrees Celsius (Table 1, 1.4).

b) Half Area of South window Shutters Unshaded

When half of the south window area (17.5m2) is left unshaded during summer days the indoor temperature increases by 0.1 to 0.6 degrees Centigrade (Table 2, 1.3). The small temperature rise seems out of proportion with the large extent of glazing area left unshaded; this is attributed to: Orientation — South orientated windows have no direct solar insolation in the summer.

Design-The optimised design of overhangs and extended vertical walls for south glazing, derived and employed at an earlier stage of the study on “Shading” [1] i. e. shade the solar aperture from the high summer sun while permitting rays from the low winter sun; the optimised design does not leave much space for any further improvement for sun control.

The temperature rise which appears in the current simulation is attributed to the decrease of thermal resistance of windows due to the absence of shutters.

c) All South Window Area Unshaded

When all south window shutters are left unshaded during summer the indoor temperature increases

at the same rate as above (0.1 to 0.5 degrees Celsius, Table 2, 1.2 and 1.3). This increase in temperature deviates from the ones succeeded with optimised design by 0.2 to 1.0 degrees Centigrade (Table 2, 1.4 and 1.2). However the indoor temperature continues to range within comfort levels (23.5 to 26.5 degrees Celsius). The maximum temperature rise (1.0 degree Celsius) reached indoors occurs in the early afternoon and evening hours between 14.00-22.00 hours (Tables 2, 1.2 and 1.4).

d) South and West Windows Unshaded

If in addition to south windows the shutters of west windows are left open during summer day the indoor temperature shows a further rise of 0.1 degree Celsius only at certain hours of the day (table 2, 1.1). The small increase is associated with the small West window area (0.50m2).

e) All Windows Shutters Unshaded

A similar rate of increase presented above (0.2 degrees) occurs when the glazed area (3.50m2) of north windows is left unshaded during the summer (Table 2, 1.0 and 1.1). The indoor temperature is maintained within comfort levels (23.8-26.6 Degrees Celsius). Maximum temperature is reached in the afternoon and early evening hours (16.00-20.00 hours). The peak temperature reaches 26.6 degrees.

Retrofitting in the historical centre of Porto vs buildings thermal regulations and energy labelling

Francisco Craveirol, Vi’tor Leal2* and Eduardo Oliveira Fernandes2

1 AdEPorto, Porto Energy Agency, R. Gongalo Cristovao, 347, room 218, 4000-270 Porto, Portugal 2Faculty of Engineering of the University of Porto, Department of Mechanical Engineering, , Rua Dr.

Roberto Frias, 4200-465 Porto, Portugal

* Corresponding Author: Vitor Leal, up. pt


Since 2006 Portugal has a new thermal regulation and since 2008 an energy labelling scheme which applies to significantly retrofitted buildings the same requirements as for the new ones. There are requirements related with the envelope and with the energy supply systems, since the nominal primary energy consumption for heating, cooling and domestic hot water is evaluated. An additional requirement is the installation of solar thermal collectors for domestic hot water heating if the cover of the building has a suitable orientation.

Recognising the specificity of historical areas, the regulation foresees the possibility of exemption of full compliance for buildings located in historical areas if justified incompatibilities are found. This paper explores the issues arising when applying the regulation to six apartments of two buildings in the historical areas of Porto undergoing a retrofitting process. The results show that it is possible to comply with the energy requirements of the regulation without interfering with the building esthetical appearance and without using solar thermal collectors. However these seem to be crucial to achieve class “A”or “A+” labels.

Keywords: Buildings, Retrofitting, Energy Labelling, Solar collectors

1. Introduction

The recently published Porto Energy Matrix [1] revealed that buildings of Porto represent about 60% of the primary energy demand of the city. The urban management and the building design thus play a decisive role in the city energetic-environmental performance. This applies to new buildings, which are a golden opportunity for doing well, but also to existing buildings, which account for most of the building stock and are crucial to achieve large-scale effects.

In the city of Porto about 1/3 of the lodges are located in the historical area of the city [2]. Although most of this area is classified as world heritage by UNESCO, most of these buildings are very old and need a retrofitting process which upgrades their value and performance as buildings on their own but also their contribution to the recuperation of the old town as quality space. In order to foster this effort of retrofitting the old town, the municipality created a special office, the PortoVivo SRU — Sociedade de Reabilitagao Urbana [3]. This work was done in cooperation with the Porto Energy Agency [4] and the SRU with the objective of assessing the compatibility of the thermal regulations with the retrofitting process. It presents a first spot assessment of the initial status of compliance with the RCCTE in the retrofitting of the Porto downtown historical residential buildings, as well as the identification of some corrective measures and the quantification of its impact in terms of the energy labelling.

The thermal regulation in place in Portugal for residential buildings is the RCCTE [5] which was adopted in 2006 as part of the legislative pack that implemented the transposition of the Energy Performance of Building Directive [6]. The regulation itself foresees the possibility of exception for buildings located in historical centres, but only if a clear demonstration of incompatibility with the patrimonial values is made.

In terms of energy requirements, the fulfilment of the regulation implies the simultaneous fulfilment of the following requirements:

i) Minimum requirements for the envelope elements (U-value and solar factor)

ii) Heating needs (useful energy, Nic) inferior to a maximum level allowed (Ni).

iii) Cooling needs (useful energy, Nvc) inferior to a maximum level allowed (Nv).

iv) Hot water needs (final energy, Nac) inferior to a maximum level allowed (Na)

v) Total primary energy (Ntc) inferior to a maximum allowed level (Nt).


Подпись: Ntc Подпись: 0.1 image418 Подпись: (eq.l)

The calculation of the total primary energy needs Ntc considers that the domestic hot water needs are satisfied at 100%, while the nominal heating and the cooling needs are only satisfied at 10% (due to use patterns). Ntc is computed as (eq.1) :

Where hi and hv represent the conversion factors from final to useful energy, while Fpui, Fpuv and Fpua represent the conversion factors from final to primary energy.

If (and only if) all the previous criteria i) to v) have been met simultaneously, then an energy class can be determined. The energy class is established through the quotient between the estimated primary energy use and its maximum allowed by regulation, with class transitions at each 25% improvement. The minimum allowed class for new or significantly retrofitted buildings is B — (table 1).

Table 1: Energy labelling as function of the relationship between the calculated primary energy use (Ntc) and

the maximum allowed (Nt).

0.75< (Ntc / Nt) < 1

0.50 < (Ntc / Nt) < 0.75

0.25 < (Ntc / Nt) < 0.50

(Ntc / Nt) < 0.25

Building energy class





Table 2 synthesises the main geometric and thermal properties of the buildings (as foreseen in the retrofitting design, i. e. the thermal characteristics are those previewed for after the retrofitting). Other important features of the buildings are the massive granitic walls and the fact that some of the surrounding streets are very narrow and do not allow significant solar incidence in some facades. Also, even in the windows with good solar exposition, the shadings are usually internal and the retrofitting designs usually try to keep this feature.

Table 3 shows the set of heating and cooling equipments considered for the calculation of final and primary energy.

Подпись: Figure 1: Case-study Buildings and its urban insertion

The first important note that was drawn from the analysis of the retrofitting design processes was that they stated right at the beginning that because the buildings where at an historical area they were exempt from compliance with the RCCTE, and therefore in most cases no effort was made to ensure compliance. The view of the authors of this article is that such an assumption cannot be taken a priory, and calculation will be made in section 3 to analyse whether there are in fact justified incompatibilities that may exempt the buildings from the application of the thermal regulation or not.

Table 2: General characterization of the buildings/apartments after retrofitting.

Building 1

Building 2

Fraction 1

Fraction 2

Fraction 3

Fraction 4

Fraction 5

Fraction 6

Number of sleeping rooms







Net floor area (m2)







External wall area (m2)







Window area (m2)







Roof area (m2)







Main orientation of windows







Envelope U value (W/m2°C)







Windows U value (W/m2°C)







Windows solar factor







Air exchange rate (h-1)







Table 3: Equipments considered in the base-case.

Equipment considered


Domestic boiler — n = 0.87


Air conditioned COP = 3

Domestic Hot Water

Gas boiler, tank poor/ insul/. n = 0.65

Photovoltaics for product designers. How designers deal with complexity of PV powered product design

D. Geelen1 , S. Y. Kan1, J. C. Brezet1

1 Delft University of Technology, Faculty of Industrial Design Engineering, Design for Sustainability
Landbergstraat 15, 2628CE Delft, The Netherlands

* Corresponding Author, d. v.geelen@tudelft. nl


How do product designers apply photovoltaic solar technology in consumer products? That question is addressed in this paper. Six design projects were analysed for the application of guidelines from the Delft Design Approach. This is a generic design approach for the design of renewable energy powered products, based on a phase model for product design, the Energy Matching Model and a Design for Sustainability benchmark. The analysis indicates that structural application of the guidelines facilitates the design process, and makes it more transparent. Further research and development for the Delft Design Approach is desirable in order to improve the development of PV powered products.

Keywords: PV powered consumer products, product design guidelines, energy matching.

1. Introduction

Imagine you are an industrial designer, and not an expert in solar energy technology, such as photovoltaics (PV). How would you design a PV powered consumer product?

This paper addresses the research question how young product designers deal with the application of PV technology in consumer products and to what extent they make use of the Delft design approach for the creation of successful PV powered products?

The Delft design approach is a generic design approach for the design of renewable energy powered products, taught at the faculty of Industrial Design Engineering of the Delft University of Technology. The approach is based on the phase model of the design process presented by Buijs and Valkenburg [1], the work on energy matching by Kan [2] and the Design for Sustainability (D4S) manual [3].

Six design projects were analysed to answer the research question. The projects discussed in this paper are recent master graduation projects executed at the faculty of Industrial Design Engineering of Delft University of Technology. All design projects were aimed to create a PV powered consumer product. All involved designers were familiar with the basis of the Delft design approach.


Mele, Edgardo1; De Benito, Liliana2; Garzon; Beatriz[12].

Architect. Chubut Rural Habitat Program Member, Instituto Provincial de la Vivienda de Chubut,

Argentina. edmele@hotmail. com

Architect. Chubut Rural Habitat Program Coordinator, Instituto Provincial de la Vivienda de Chubut,

Argentina. lilianadebenito@yahoo. com. ar

Architect. FAU-SeCyT Universidad Nacional de Tucuman Project Director. CONICET Investigator. Member of Chubut Rural Habitat Program, Instituto Provincial de la Vivienda de Chubut, Argentina.

bgarzon@gmail. com


The purpose of this work is to develop a model of management and production of solar houses build by the State so as improve life conditions for rural settlers in three villages in Chubut, in southern Argentina. These dwellings show the development of architectural prototypes, suitable to geographical and climatic rigorous conditions. The prototypes incorporate appropriate technology (soil-cement, rubblework, solar cover collectors, etc.); the possibility of using forms of renewable energies such as solar to heat water or air, to cook, to dry clothes or as aeolian energy to generate electrical energy; the rational use of the firewood as fuel and assisted attended auto-construction. The Methodology selected is the Participative Action Research. It has been used not only to acknowledge this reality but to transform it. The participation of the people involved as well as instruments for changing their reality. The bioclimatic guidelines and strategies as well as the architectural covering and dwellings’ architectural typology for their climate adaptation and the proposed technological systems have been determined and assessed. These houses have built with the conjoint effort of both the beneficiaries working co-operatively and the team of technicians in charge of the project. The realization of this project has been possible thanks to the users’ enthusiastic and highly qualified participation in the appropriation of alternative technological systems. It is thanks to these systems that the necessities and/or environmental, technological, and functional conditions of families and communities have been attended to strengthening at the same time, the concept of belonging and evaluating a re-evaluating a community’s natural and cultural milieus.

Key Words: Domestic Rural Habitat, Sustainable Building Adequateness, Social Interest Solar House.

Energy balance of rooms at attics

The model of unsteady energy transfer through, outside and inside building elements has been developed [1]. In order to reduce the number of variables to a level that allows different design options of a room to be compared in a meaningful way it has been useful to make some simplifications. A fixed room size (16 m2) and room temperature requirement (constant in time and space, equal to 200C) have been assumed. The model of unsteady energy transfer outside, through and inside the wall has included heat conduction and heat capacity of wall elements, heat convection with indoor and outdoor room surrounding, and radiation exchange between indoor and outdoor room surrounding and the wall. Solar radiation absorption and reflection on wall surfaces, and the effects of orientation and inclination on them have been considered.

The energy balance of a room includes energy transferred through opaque and transparent elements, including direct transfer of solar energy through windows, energy needed for ventilation, and energy supplied by the internal heat sources. It has been assumed that energy supplied by the heating/cooling system (HVAC) is treated as internal heat source. According to assumption made, the indoor temperature is constant in time and space. It means that HVAC system operates all the time providing required (by the constant indoor temperature) heating or cooling energy. The mathematical model developed has been used for numerical simulation using Matlab as the programming language. It allows many cases of different location of rooms to be evaluated. Selected results of simulation studies of attic rooms are presented in Fig. 5-8. Figures 5-8 present distribution of heating/cooling demands for the whole averaged year (averaged curves for every month) with the south and north inclined envelope with small and big windows, respectively.

For the south orientation the maximum hourly cooling demand is at noon in July and August and for a room with the small window it is about 1,3 MJ and with the big window it is about 5,5 MJ. There is no cooling demand from November till January for the room with the small window. Apart from these months during a day time there is need for cooling. Duration of cooling mode depends on the month of the year and depends on solar irradiance and ambient temperature. For the room with the big south window all year round during day time there is need for cooling (different number of hours of operation of the cooling system for different months). In winter there is heating demand with maximum early in the morning (about sunrise) in January and it accounts to 0,8 MJ/h for the room with the small window and to 1,8 MJ/h for the room with the big window.

For the north orientation the maximum hourly cooling demand is at noon in July and June and for a room with the small window it is about 0,7 MJ/h and with the big window it is about 2,8 MJ/h. There is no cooling demand from October till March for the room with the small window. In the rest of the year during a day time there is need for cooling, the duration of cooling mode depends on the month of the year (because of the level of solar irradiance and ambient temperature). For the room with the big south window there is no need for cooling from October till February, during the rest 8 months the cooling mode exists with different operation time. In winter there is heating demand with maximum early in the morning (about sunrise) in January and it accounts to more than 0,8 MJ/h for the room with the small window and to 1,8 MJ/h for the room with the big window.

It is evident that night heating demands are resulted from the ambient temperature fluctuation. Heat losses are mainly through windows. Opaque walls have the designed thermal capacity. Heat stored during day time influences indoor climate in the night. During day time the influence of solar radiation and energy transferred through windows is evident. Solar radiation causes need for cooling in summer and reduces heating demand in the rest of the year. Solar gains could be so high that there is no need



for heating for a few or several hours per day. It is remarkable that shapes of curves of solar radiation through windows (Fig. 1-4) are similar to curves of energy demands (Fig. 5-8) during the day time.

Fig. 5. Distribution of daily heating/cooling energy demands for all months, south room with small window

x 106 Heat balance of the room, with X = 0.52, Beta= 45, Gamma = 0 Xt = 2Yt = 2

——- Jan





— Jul Aug

— Sep Oct

— Nov

— Dec




2. Conclusions

Figures 5-8 show daily distribution of energy required per hour to meet the heating/cooling demands of the rooms under consideration. Table 1 presents the sums of seasonal heating/cooling demands in the form of seasonal energy indexes (energy required to meet heating/cooling demands for the whole heating or cooling season with regard to 1 m2 of the room floor area). The space heating energy consumption indexes are below limits given by national standards (72,5 kWh/(m3a)). No regulations exist for space cooling indexes, however, it is evident that they are very high and limits for space cooling should be introduced as soon as possible.

Table 1. Seasonal energy consumption indexes for rooms at attics with different orientation

Seasonal energy consumption indexes





Eh — space heating






Ec — space cooling






Eh+Ec — total






Other results of simulation studies show that cooling season for south, east and west oriented attic rooms (floor area 16 m2, external wall area 12 m2, 3 layers, Uwall= 0,3 W/m2K, window — 4 m2, Uwin=1,6 W/m2K) lasts 8, 6 and 6 months and the cooling demands are about 5500, 3800, 3300 MJ per season respectively. The heating season for the same rooms lasts 4, 6 and 6 months and the heating demands are about 2000, 2700, 3000 MJ per season respectively. In all cases cooling demand is higher than heating demand, for the south room even nearly three times, which is surprising for high latitude country (Warsaw 520 N).

It appears that overheating in summer due to high solar irradiation and energy transmitted and absorbed in glazing can be a real problem for rooms in attics. To assure stable indoor thermal comfort of rooms in attics (mainly to avoid overheating, according to the assumptions made in the model), i. e. to keep a constant temperature in the rooms under consideration, it is necessary to use shading, e. g. external blinds. If no shading is applied then air-conditioning systems, which are usually electrically driven and consume a lot of primary energy, must be used. Of course there is one simple conclusion: not use the attic spaces for living spaces.


[1] D. Chwieduk, (2006). Modelowanie i analiza pozyskiwania oraz konwersji termicznej energii promieniowania slonecznego w budynku. IFTR Reports, 11/2006, Warszawa.

[2] D. Chwieduk, Some Aspects of Modeling the Impact of Solar Energy on the Energy Balance of a Room, Solar Energy (in print).

[3] D. Chwieduk, B. Bogdanska, Some recommendations for inclinations and orientations of building elements under solar radiation in Polish conditions, Renewable Energy Journal, 29 (2004) 1569 — 1581.

[4] S. Sherbiny, G. Raithby, K. G. Hollands. Heat transfer by natural convection across vertical and inclined air layers, Journal of Heat Transfer 104 (1982) 96-102

[5] D. T. Reindl, J. A. Duffie, W. A. Beckman, Evaluation of Hourly Tilted Surface Radiation Models, Solar Energy, 45 (1999) 9 — 14

Study Framework

An increasing interest and application of the glass material in architecture and Portuguese construction can be observed through the buildings of the built where it is more used in the service buildings-Fig.1.

It is a common sight in the service buildings (mainly office buildings) built in the last decades, the glass material as constituent part of the envelope and in considerable proportions. The residential buildings, usually present, lower glazing areas than the service buildings. Meanwhile, it is possible to note a growing increase in the glazing areas in the facades of the residential buildings built in the last decades (Fig. 2), and even, some of the residential buildings built in the last years have practically glassed facades similar to the service buildings, see Fig. 3.




Подпись: Fig. 3. Residential buildings with glass facades (Lisbon, last years).

Fig. 2. Evolution of residential buildings and glazing areas in the last decades (Valmor Awards).

Large glazing areas in residential buildings are architectural solutions or options that allow a more homogeneous exterior aesthetic view, scenery contemplation, greater transparency and luminosity; while having a direct influence in the comfort of its occupants, and are determinant for the building thermal-energetic performance (large glazing areas in a residential unit increases the potential for heat gain or loss). The residential buildings highlighted in Fig. 3 were selected for this study. Some flats of these buildings were monitored through the summer (2007) and winter (2007-2008). In this way this work will show the main results and observations of the monitoring.